what axel ratio to pick?

warholic · 07-11-2009, 02:10 PM

Hi all - i searched but couldn't find a thread so here goes:
I'm buying a V10 gasoline RB 50 van and I'm trying to determine which axle ratio to get - 3.73 or 4.10. I won't be towing anything, or if I EVER did it would be an itty bitty trailer. But I will be outfitting the van with the SMB 4x4 upgrade and the "50" plan or similar, and other stuff. My understanding is better gas mileage with the taller 3.73 ratio...
the example is with 2 identical stock vans, the only difference being one has 3.73 and the other van has 4.10, at 55 mph the 3.73 axle might run about 2200 rpm and the 4.10 axle would run about 3100 rpm.
I'm thinking the 4.10 is really for towing stuff.
I have a question into SMB because I don't know if this affects their 4x4 upgrade so I will cover that base.
I also know with 4x4 conversion and bigger tires/rims, I will have to modify speedo and/or gearing in diffs to get speedo reading right. I would think either ratio would have same impact in terms of necessity for and cost of these mods to correct speedo, so that seems a wash.
thx
warholic

**daveb** · 07-11-2009, 04:13 PM

I'm happy with 4.10's (I think that's what SMB normally installs) & 285's but if I were to install larger tires I would probably go bigger (lower gears) than 4.10's. Kind of depends on what you're gonna do with the van and how heavy you plan to load it. I have a diesel so low end torque is there for me while in low range and fuel economy is reasonable. The diesel also has good engine braking so the 4.10's are about right for downhill grades when not pulling a trailer. Not too sure about the V-10's downhill prefomance with 4.10's but it's probably better while climbing steep grades at highway speeds compared to the diesel.
Dave

warholic · 07-11-2009, 04:52 PM

Hey daveb - I'm guessing you have 285/70R17s?
Since your diesel came with 4.10s and SMB uses 4.10s in their 4x4 mods, did you have to adjust your speedo ........ or gears ? ......... because the stock tires are smaller 16s before the mods by SMB.

**BroncoHauler** · 07-11-2009, 06:01 PM

Warholic,

Shouldn't a 10% gear ratio change, give you a 10% RPM change? I think your math is a bit off.

Herb

**daveb** · 07-11-2009, 06:02 PM

No they are 16". I'm not sure if 17's would make that much difference. I had SMB adjust the speedometer before I picked it up but it still is about a mile and a half off according to GPS (at 55, I'm really 54). No big deal and as much time as I am in low range the mileage is off anyway.
Dave

Ford_6L_E350 · 07-11-2009, 06:10 PM

The difference between 4.10 and 3.73 is only about 10%. So the difference in rpm's is only about 10% - 2200 vs. 2000rpm for example.

Personally, I think 3.73 is a good gear ratio. Unfortunately, when I ordred my van the choices were 4.10 or 3.55, so I went with 4.10. Both my pickupshave 3.73 gears.

Mike

JoeyNick · 07-12-2009, 12:36 AM

These vans are heavy. Go with the 4.10 for better torque and if you want to make the gears "taller", go with taller tires.

Stumpalump · 07-12-2009, 01:32 PM

4.10 unless you can get the 4.30 as an option. You can read all about the V10 and find gear threads here:http://www.ford-trucks.com/forums/forum49/ The newest V10's like high RPM's so lower gears are best.
http://www.ford-trucks.com/forums/forum49/

warholic · 07-12-2009, 09:39 PM

Thx for all the responses ...... of course, good input on both ratios!

Stumpy - I went to the sight and looked for 20 mins - couldn't fine any blog on gears ratios. I'll try again - maybe I'm missing something?

Anyway, 4.10 seems to be overriding reccomendation.

Stumpalump · 07-12-2009, 09:58 PM

I started a thread for you. http://www.ford-trucks.com/forums/86723 ... ost7711698
What tire height is going on your rig?